Process for preparing oxamide



including the pyrolysis of ammonium'oxalate.

Patented July 21, 195 3 TENT OFFICE PROCESS FOR PREPARING OXAQMIDE Jack Daniel Jofle, Hopewell, and Leland James Beckham, Bermuda District, Va., assignors to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application February 21, 1950, Serial No. 145,596

13 Claims. (01; 260-561) l 2 g This invention relates to a process for prepar- The main reaction in the pyrolysis of aming oxamide by the pyrolysis of ammonium'oxamonium oxalate to oxamide, proceeds as follows: late, and more particularly to a process for carry-ing out the reaction in the presence of an acidic phosphorus-containing catalyst.

Oxamide is useful as a fertilizer. It has been prepared in the past by a number of processes As carried out 1D. the past, however, in the Ammonium Oxalate Oxamide absence of a catalyst, the pyrolysis of ammonium oxalate resulted in only small yields of oxamide, for example of not more than about 28% of theoreti l petitive with several other reactions, as is well It is an object of this invention to provide a known, whichtake place to some extent within process for preparing oxamide by the pyrolysis of the temperature range specified to produce as ammonium oxalate, in higher yields than have end products, ammonia, formic acid, CO2, CO, been obtained heretofore, and in a state of high etc. We have found that by carrying out the P ity. pyrolysis of ammonium oxalate in the presence This and other objects are accomplished according to our invention wherein ammonium at temperatures within the range specified above, oxalate is subjected to pyrolysis in the presence and preferably within the range between about of an acidic phosphorus-containing catalyst. 180 C. and about 200 0., competing reactions In carrying out the process of our invention, are minimized relative to the desired reaction, ammonium oxalate (i. e. diammonium oxalate) and high yields of oxamide of high purity are and an acidic, phosphorus-containing catalyst obtained. At temperatures below about 180 C., are mixed and are heated in a suitable vessel to the illustrated reaction is inconveniently slow, temperatures between about 155 C. and about while at temperatures above about 200 C., cer- 220 C. for the length of time desired, preferably tain of the competitive reactions, wherein CO2, for the length of time (at the temperature em- CO and NH3 are produced, are sharply increased, ployed) required for obtaining the optimum yield with an accompanying drop in the yield of of oxamide. During the course of the pyrolysis, oxamide. the water of reaction may be condensed from The catalysts useful in our reaction are acidic, the vapors formed in the'pyrolysis and a periodic phosphorus-containing compounds, such as'any determination of the volume of water evolved of the phosphorus acids, their anhydrides and serves as a measure of the rate at which the 5 acid salts of alkali metals and ammonia and pyrolysis reaction is proceeding, The solid, subinclude the following: stantially water-insoluble oxamide resulting from the pyrolysis remains in the pyrolysis vessel and is removed therefrom as such after substantial completion of the reaction, and maybe separated from associated water-soluble impurities by washing with water to dissolve such impurities, and mechanically separating the solid, insoluble oxamide from the water solution containing the impurities.

The desired reaction illustrated above is com- P2O5phosphorus pentoxide (phosphoric acid anhydride) NaI-I2PO4--monosodium phosphate NI-I4H2PO4-m0noammonium phosphate (NI-l4) zI-IPOa-dfimmonium phosphate The relative effects of these catalysts in comparison with a comparable run in which no catalyst was used are illustrated in Table I below.

, TABLE I Efiect of'catalysts on production of oxamidev- Catalyst flours Product) Percent Theor.

of an acidic, phosphorus-containing catalyst, and

TABLE II Efiect of particle size of ammoniamomalate and catalyst on yield of omamide o c 1 t ONE i i of yiemdoxl a a ys 4 2 eacarm e, Catalyst Mesh 1 Mesh 1 tion, Percent Hours Theor.

N&HZPO4.H20 100 100 3. 5 72. 9 NaHzPO4.H2O 10 10-10 3. 5 71. 7- NQH2POLHZO. 30-40 1040 5 64.0 NaH POi.HzO 30*10 100 5. 5 58. 4

1 The values given show the screen size of particles in meshes per linear inch.

The charge is preferably mixed dry, and for this purpose anhydrous ammonium oxalate may be used. However, the hydrated ammonium oxalate of'commerce ((COONI'Li) 21-120) may be used, and the water removed during the pyrolysis. When P205 is used as the catalyst, however, we find it advantageous to mix the charge slightly wet to facilitate intimate mixing.

Any desired quantity of acidic, phosphoruscontaining catalyst may be used to exert a promoting action upon the desired pyrolysis reaction illustrated. However, we prefer to use quantities equal to at least about 4% by weight of the charge to gain an appreciable promoting action, and generally quantities of not more than about by Weight of the charge are sufficient to give optimum yields consistent with practical operation. Usually a quantity of catalyst between about 5% and about 10% by weight of the charge is suflicient. The effect of varying catalyst quantity is illustrated by runs tabulated in Table III below.

TABLE III Effect of catalyst quantity on rate of pyrolysis of V ammonium oxalate to oaamide and on yield of oxamicle.

Our reaction is preferably carried out at normal atmospheric pressures or somewhat below. We find that pressures appreciably in excess of atmospheric (5170 mm. Hg) decrease the rate of reaction somewhat, while pressures below atmospheric down to about 200 mm. of mercury increase the rate of reaction slightly. Representative results are tabulated below in Table IV.

TABLE IV Effect of pressure on the rate of pyrolysis of ammonium oxalate to omamide Weight Absolute Y l Catalyst Percent o Pressure lgfg Catalyst mm. Them,-

N3HzPO-1.H20 5 17 200 5170 52. 4 NZHZP 04.H2O 5 4 198 760 71. 4 NlflH2POLHzO- 5 5. 2G0 3-6 50 NH4H2PO4 10 4. 25 185 200 71. 6 NH4H2P04Q 10 G. 5 185 760 84. 3

The rate of the reaction in the pyrolysis of ammonium oxalate to oxamide varies markedly with the temperature. We have found that the pyrolytlc dehydration of ammonium oxalate to oxamicle is a half order reaction which may be expressed according to the following equation (MAO) dt TABLE V Effect of temperature on rate of pyrolysis of ammonium oxalate to oxamide Yield Weight Time of Temp, "0. Catalyst Percent Reaction, 53E32 Catalyst Hours The 200 NH4HZPO4 4 4 75. 1 NH4HQPOLU; 4 10 79. 5 172 kHiHgPoinn 17 76. l

We have further found that an undue prolongation of time of reaction has a harmful eifect on yield of oxamide as illustrated in Table VI below.

TABLE VI Efiect of increase of reaction time on yield of oxamz'de 1 water of pyrolysis.

Accordingly, we prefer to carry out, the pyrolysis for periods not more than about hours, and preferably for periods between about 2 and about 7 hours at the temperatures specified even though the reaction is not theoretically complete as measured by the amount of water of pyrolysis collected.

The following specific examples further illustrate our invention.

EXAMPLES 141 There are listed below in Table VII the conditions employed and the results obtained of working Examples 111 inclusive, run according to the general procedure set forth below, with the variations noted in the table, using a charge of anhydrous ammonium oxalate, together with a catalyst of the character contemplated by the invention. For comparative purposes, there are also listed at the end of the table, data covering a control run made under comparable conditions, but without a catalyst.

The runs of these examples were carried out by placing a charge of solid, anhydrous ammonium oxalate and catalyst in the quantities and fineness indicated, in a U-shaped pyrolysis .tube, fitted with a thermocouple for recording inside temperature, and having one arm closed ofi with a stopper. Attached to the other arm of the U-tube was a sublimation tube consisting of an air-cooled condenser for condensing the After charging ammonium oxalate and catalyst, the pyrolysis tube was placed in a heated oven, equipped with means for maintaining the temperature within 3 C. of the desired value. When the pyrolysis tube wash in position in the oven, the sublimation tubeconnected thereto extended through an aperture in the oven, and was connected in turn to a graduated cylinder, surrounded by an ice bath, to collect and condense the water of pyrolysis. The apparatus was also provided with acid and about minutes and the temperature was main- 'tained at about this value for the period indicated.

The vaporous products of pyrolysis formed as the reaction proceeded-mainly water, NHa. CO2 and COwere led through the sublimate tube where the water of pyrolysis condensed, then through the acid and base bubblers to absorb N113 and CO2 respectively. The exit gas was mainly CO. The water condensed in the sublimate tube was led to the graduated cylinder where volume of water of pyrolysis was read and recorded at minutev intervals and served as a measure of the rate of reaction. Tare weights of pyrolysis tube, sublimation tube and graduated cylinder were recorded before the reaction and weight differences were recorded at thecompletion of each run.

The solid residue, consisting mainly of oxamide, remaining in the pyrolysis tube was washed out of the tube with water, and the mixture was heated to 90 C. to dissolve the water-soluble base absorption vessels (bubblers) for absorb- After the charged tube was placed inthe oven,

it was brought to the desired reaction temperature, as indicated in the table, in a period of impurities to facilitate their separation from the substantially water insoluble oxamide. The

mixture was then cooled to 30 C. to further decrease the solubility of the oxamide, then. filtered. To further purify the water-insoluble oxamide residue, it was again mixed with water, heated to 90 C., cooled to 30 C. and filtered. The recovered solid oxamide product was first The product was assayed for oxacid to oxalic acid, and titrating with KMnO4. It will be observed that in the majority of the runs, an assay of 98% or more was obtained,

in agreement with the theoretical values for pure oxamide withinthe limits of experimental error. It is, therefore, apparent that our process yields a virtually pure oxamide product. It will be noted that yields of oxamide obtained in the runs'of Examples 1-11 inclusive ranged from to of theoretical, whereas that obtainedin the run in which no catalyst was used gave a yield of only 28%. 1

TABLE VII using Oven Insoluble L gth i CProdutctd Mfi terial Grams Cata- Cataen 9 one: 6 Percent Percent i (000N114); g t Catalyst lyst, lyst, 1 3 2%? ggf Oxamidc Oxa mide Anhydrous Grams .Mesh Hours Solubility Perceznt Assay c Yleld in Extract Input b Liquor d NaHzPO4.H O- 5. O 200 14. 1 78. 4

P305 I 5. 0 200 11. 8 66. 4 P305 3. 0 219 11. 2 63. 0 NB.H2POA.H O 4. 5 196 14.2 80.0 NaH2PO4.Hz0- 4. O 197 12. 0 67. O NEHzPOLHZOnH 17 172 13. 89 76. 1 P205 4. 5 201 11. 57 59. 5 P205 4. 5 197 12. 74 66. 8 P205 Z 2 197 13. 22 68. 6 N3H PO4.H2O 4 198 13. 73 71. 4 NaH2PO4.H20---- 6. O 200 5. 29 50. 0 N 7. 0 19s 5.1 28.6

I For footnotes tothistablasee Table VIII.

.. EXAMPLES 12-25 Examples 12 to 25, conditions and results of which are listed in Table VIII below, were carried out in a manner similar to that described for Examples 1-11 above, except that a molten wax bath was substituted for the oven as the heating unit. g

The conditions under which these examples were carried out and the results obtained are iven below.

period of not more than about 10 hours.

4. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a catalytic quantity of an inorganic acidic phosphorus-containing compound selected from the group consisting of phosphorus acids, anhydrides of phosphorus acids and alkali metal and ammonium acid salts of phosphorus acids and heating the resulting mixture at a temperature be- TABLE VIII Pyrolysis of ammonium oxalate in the presence of variou catalysts under various conditions of temperature, time and fineness of charge, using was: bath Insoluble Product Material Grams I Qata Lengthoi Corrected Unac- Percent Percent Example (C ONH Mesh Cam] st lvst Catalyst, Pyroly- Temp, For Oxacounted Oxa Oxa- No. Anh g (C O ONE-02 y Gian'lS Mesh sis in C. mide Solu- For Permide midc Y Hours. bility In cent In- Assay 0 Yield Extract put b Liquor d 12 25 (lggrllliolar, NH4H2P04 1.0 50-80 4 v 200 14. 36 0.8 98. 3 75.1 13 25 ,.,do NH4HzPO4 1.0 50-80 10.25 185 15. 62 0 95. 3 79.5 14 (NH4)2HPO4 1. 1 40-80" 3. 200 12. 86 5. 4 98. 3 71. 0 15 NHlHzPO4 1. 0 50-80 4. 25 200 14. 09 90. 0 70. 7

16 50 ""110 NH4H2PG4 2. 5 50-80 5. 25 200 28. 51 2. 7 96.1 77 17 25 Powdered, NH4H2PO4 2. 5 Powdered, 6. 5 185 15. 30 1.1 98.0 84. 3

80-100. 60-100. '18 25 G r1l&1ar, NH4H2P04 1.0 50-80 10 200 12. 72 3. 5 99.4 71. 0 2 l9 25 Powdered, NH4H2PO4 3. 75 Powdered, 6. 75 185 15. 72 1.4 97.5 86.1

80-100. 60-100. 20 100 G g anillar NE-iHZPOA V 4. 0 50-80 8. 75 194 57. 98 2.1 95. 6 77. 9

21 Pgzglgged, NaHzPO4.H2O 3. 75 60-100 6. 185 14. 43 0 99. 0 80. 3 22 25 Q d0 NH4HzPO4 6. 25 50-100 5. 5 185 15.47 1.3 98.2 85.4 23,; 25 Gg l%&1ar, NHJHQPQq 1. 25 50-80 11 200 7. 58 98.2 42.3 24 25 Pggdged, NHlHgPO; 2. 5 60-100 5 185 13. 87 4.4 98. 0 7G. 4 25 2 5 ,do NH4H2PO4 2. ,5 60-100 4. 25 185 13. 28 96. 0 71. 6

a Time required to collect maximum amount of water. b Values exclude weight of catalyst used in each reaction.

6 For purposes of calculation, the solid sublimate was considered to be (NHmCOLHrO. d Figures include solubility of oxamide (0.23 g. oxamide/500 ml. H2O at 30 0.).

1! Catalyst and oxalate mixed dry in Example 7.

1 Several drops of 1320 added to catalyst and oxalate in Example 8.

8 Catalyst and oxalate mixed with 25 ml. H2O in Example 9. Reaction carried out at low pressure (2-15 mm. abs. range). oxamide i The values given show the screen size of the particles in meshes We claim:

1. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the step which comprises heating solid ammonium oxalate in the presence of a catalytic quantity of an inorganic acidic phosphorus-containing compound selected from the group consisting of-phosphorus acids, anhydrides of phosphorus acids and alkali metal and ammonium acid salts of phosphorus acids at a temperature between about 155 C. and about 220 C.

2. In a process-for preparing oxamide by the pyrolysis of ammonium oxalate, the step which comprises heating solid ammonium oxalate in the presence of a catalytic quantity of an inorganic acidic phosphorus-containing compound selected from the group consisting of phosphorus acids, anhydrides of phosphorus acids and alkali metal and ammonium acid salts of phosphorus acids at a temperature between about 180 C. and about 200 C. l

3. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a catalytic quantity of an inorganic acidic phosof phosphorus acids and alkali metal and ammonium acid salts of phosphorus acids and heating the resulting mixture at a temperature be- Insoluble residue was considered 100% oxamide and sublimate titrated for per linear inch.

tween about 180 C. and about 200 C. for a period between about 2 hours and about '7 hours. 5. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of an inorganic acidic, phosphorus- :containing compound catalyst selected from the group consisting of phosphorus acids, anhydrides of phosphorusacids and alkali metal and ammoniumacid salts of phosphorus acids equal to between about 4% and about 15% by weight of the charge, and heating the resulting mixture at a temperature between about 180 C. and about 200 C., at a pressure between about 200 mm. of mercury and about 760 mm. of mercury for a period between about 2 and about '7 hours.

6. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of monoammonium phosphate, equal to between about 4% and about 15% by weight of the charge and heating the resulting-mixture, at a temperature between about 180 C. and about mercury and about 760 mm. of mercury for a period between about 2 and about '7 hours.

7. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of monosodium phosphate, equal to 9 between about 4% and about 15% by weight of the charge, and heating the resulting mixture at a temperature between about 180 C. and about 200 C., at a pressure between about 200 mm. of mercury and about 760 mm. of mercury for a period between about 2 and about '7 hours.

8. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of diammonium phosphate, equal to'between about 4% and about 15% by weight of the charge, and heating the resultingmixture at a temperature between about 180 C. and about 200 C., at a pressure between about 200 mm. of mercury and about 760 mm. of mercury for a period between about 2 and about 7 hours.

9. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of phosphorus pentoxide, equal to between about 4% and about 15% by weight of the charge, and heating the resulting mixture at a temperature between about 180 C. and about 200 C., at a pressure between about 200 mm. of mercury and about 760 mm. of mercury for a period between about 2 and about 7 hours.

10. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a quantity of phosphoric acid, equal to between about 4% and about 15% by weight of the charge, and heating the resulting mixture at a temperature between about 180 C. and about 200 C., at a pressure between about 200 mm. of mercury and about 760 mm. of mercury for a period between about 2 and about 7 hours. I

11. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the step which comprises heating solid ammonium oxalate in the presence of a catalytic quantity of an inorganic acidic phosphorus compound selected from the group consisting of phosphorus acids, anhydrides 10v of phosphorus acids and alkali metal and ammom'um acid. salts of phosphorus acids, at a temperature between about 180 C. and about 200 C. for a period of not more than about 10 hours.

12. In a process for preparing oxamide by the pyrolysis of ammonium oxalate, the step which comprises heating solid ammonium oxalate in the presence of between about 4% and about by weight based on the weight of the charge of an inorganic acidic phosphorus compound selected from the group consisting of phosphorus acids, anhydrides of phosphorus acids and alkali metal and ammonium acid'salts of phosphorus acids, having a particle size such that all passes a mesh screen, at a temperature between about C. and about 200 C. for a period of not more than about 10 hours.

13. In aprocess for preparing oxamide by the pyrolysis of ammonium oxalate, the steps which comprise mixing solid ammonium oxalate with a catalytic quantity of an inorganic acidic phosphorus compound selected from the group consisting of phosphorus acids, anhydrides of phosphorus acids and alkali metal and ammonium acid salts of phosphorus acids, and heating the, mixture at a temperature between about 180 C. and about 200 C. for a period of not more than about 10 hours. JACK DANIEL JOFFE. LELAND JAMES BECKHAM.

References Cited in the file of this patent UNITED s ATEs PATENTS Number Name Date 1,582,675 Fick Apr. 2'7, 1926 1,872,700 Dreyfus Aug. 23, 1932 OTHER REFERENCES 

1. IN A PROCESS FOR PREPARING OXAMIDE BY THE PYROLYSIS OF AMMONIUM OXALATE, THE STEP WHICH COMPRISES HEATING SOLID AMMONIUM OXALATE IN THE PRESENCE OF A CATALYST QUANTITY OF AN INORGANIC ACIDIC PHOSHOROUS-CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHOSPHOROUS ACIDS, ANHYDRIDES OF PHOSPHOROUS ACIDS AND ALKALI METAL AND AMMONIUM ACID SALTS OF PHOSPHOROUS ACIDS AT A TEMPERATURE BETWEEN ABOUT 115* C. AND ABOUT 220* C. 